text: Epoxidations of alkynes and allenes proceed by concerted mechanisms analogous to epoxidations of simple alkenes. Often, these epoxidized products are unstable and undergo further oxidation reactions via different mechanisms, such as Y-H insertion.
  Kinetic studies of heteroatom oxidations have demonstrated that their mechanisms likely proceed by an S2 process, rather than a single-electron-transfer pathway. An example of heteroatom oxidation is the nucleophilic decomposition of DMD by N-oxides, a side reaction that regenerates the reduced starting material and converts the oxidizing agent to dioxygen and acetone. 
  Concerning the mechanism of C-H and Si-H oxidations, two mechanisms have been proposed. The debate centers on whether the oxidation takes place via concerted oxenoid-type insertion or via radical intermediates. A large body of evidence (including analogous oxidations of alkenes and peracid epoxidation) supports the concerted mechanism; however, recent observations of radical reactivity have been made. Complete retention of configuration in oxidations of chiral alkanes rules out the involvement of free, uncaged radicals. However, products of radical decomposition pathways have been observed in some DMD oxidations, suggesting radical intermediates.